I'm cleaning a repacking a rear wheel from a 1981 Miyata 1000 that fell into my hands a while back (that is, the whole bike did, not just the wheel). It has Sunshine Gyromaster hubs--the first set I've worked on, I think. I was surprised to find that the dust cover flange on the non-drive side in back has what seems to me an unusual shape. It's pressed inward, toward the bearing balls, giving it a sort of funnel shape. I hope that's visible in the picture.

My first thought was that it had been bent or damaged somehow. It's easy to damage dust covers in prying them out, but in my experience that usually causes them to be bent outward, not inward as this one is. Also, it doesn't look accidental, because it's perfectly uniform all the way around. I think the dust cap was made that way.

Another oddity is that the dust-cap opening seems to be a very loose fit around the cone. (I know the cone is facing the wrong way in the photo--I just placed it that way to compare its size to the size of the opening in the dust cover.) Possibly either the cone or the cover is not original to the hub? I can't say.

So here's the question: Is this a feature of Gyromaster hubs, and if so why? And why does only the non-drive-side feature this type of dust cover? Both of the front covers and the cover on the drive side are the conventional flat variety.

I'm not going to sweat this too much. Unless someone gives me a good reason not to I'll just clean and repack the hubs and try not to think about the slightly wide gap between cone and the dust cover. But I can't help being a little curious about it. Has anyone out there seen this kind of thing before?